To date, few three-wheeled straddle-type vehicles have been produced commercially for road use. One possible configuration of such a vehicle consists in having two wheels at the front of the vehicle and one at the rear of the vehicle. The vehicle has to be provided with a frame to mount the wheels and the various components of the vehicle, such as the engine, air box and fuel tank.
One previous type of vehicle frame, known as a space frame or a ladder frame, has been used in all-terrain vehicles (ATVs) having four wheels. FIG. 1 illustrates such a frame 850. The frame 850 includes a spaced pair of upper tubular members 852, 854 and a spaced pair of lower tubular members 856, 858. The upper and lower members 852-858 are interconnected by respective spaced pairs of cross members 860, 862 and 864, 865. Respective pairs of the upper and lower members 852, 854 and 856, 858 are connected by laterally extending cross members 866 (connecting the upper members 852, 854) and cross members 868 (connecting the lower members 856, 858). A plate 870 is connected between the lower members 856, 858 to thereby add additional rigidity between the lower members 856, 858.
As can be seen in the example described above in FIG. 1, these frames have been either complex or have used a large amount of material, or both. It is possible to construct the frame with high strength metal alloys to increase strength properties of the frame without relatively increasing the weight. However, these metal alloys are costly and some require additional processing steps (such as post-weld heat treatment) in the manufacture of the frame.
Another type of vehicle frame is disclosed in U.S. Pat. No. 6,799,781, assigned to Bombardier Recreational Products Inc. The frames described therein are less complex and costly than the above-mentioned space frames. This is achieved by using a plurality of central beams to make up the frame. However, these frames were developed for ATVs which are generally operated off-road at reduced speeds. Road vehicles must operate at much higher speeds (100 km/h or more) and their frames are therefore subjected to greater forces. The frames described in the '781 patent may not be able to resists these high forces. They could be modified to increase the size of the central beams or by using stronger materials but this would result in increased costs and most likely in an increase in weight as well.
As shown in the '781 patent, the frames described therein were designed for four-wheeled ATVs which typically use a McPherson suspension for the front wheels. This type of suspension can easily be accommodated by the described frames. However, straddle-type three-wheeled vehicles are intrinsically less stable than four-wheeled vehicles (but it should be noted that the lower stability of a three-wheeled vehicle versus a four-wheeled vehicle should not be understood to mean that a three-wheeled vehicle is unstable to the point that it is dangerous to a user). For this reason, it is preferable that the front wheels of a three-wheeled vehicle should use a type of suspension that helps controlling the roll or sway of the vehicle more than a McPherson suspension.
All of the above-mentioned frames were developed for ATVs and as such do not satisfactorily respond to the previously enumerated needs of straddle-type three-wheeled vehicles for road use.
Therefore, there is a need for a frame which addresses some of the needs of a straddle-type three-wheeled vehicle having two front wheels.
There is also a need to provide a straddle-type three-wheeled vehicle for road use which has a relatively simple frame while providing the strength requirement for such an application.
There is also a need to provide a straddle-type three-wheeled vehicle for road use with a frame which can accommodate a front suspension that helps controlling the roll or sway of the vehicle.
Also, three-wheeled vehicles having two front wheels and one rear wheel do not have as much room to accommodate components in the rear portion thereof as four-wheeled vehicles, such as ATVs, due to their reduced width at the back. Therefore, the vehicle components, such as the engine, air box, and fuel tank, cannot be arranged in the same manner. Thus, there is also a need for an arrangement of the vehicle components which is suitable for the space limitations of a straddle-type three-wheeled vehicle having two front wheels while maintaining accessibility to the components which require it.